Many different acoustic resonator devices have been developed. Known Bulk Acoustic Wave (BAW) resonators include one or more piezoelectric layers disposed between two electrodes. For example, thin Film Bulk Acoustic wave Resonators (FBARs) typically include a single piezoelectric layer between two electrodes. Stacked thin film Bulk Acoustic wave Resonators (SBARs), on the other hand, typically include two piezoelectric layers disposed between top and bottom electrode layers and separated from each other by a middle electrode, which typically is used as a grounding electrode. Some acoustic resonator devices include multiple acoustic resonator devices that are isolated from one another by one or more isolation layers.
A BAW resonator has a resonant frequency that is determined primarily by is the thickness of the piezoelectric layer and secondarily by the thicknesses and the materials used for the other layers. A BAW resonator typically is acoustically isolated from the supporting substrate by an isolation structure, such as a cavity formed under a membrane supporting a BAW resonator or an acoustic mirror consisting of a stack of layers alternately formed of high and low acoustic impedance materials and having respective thicknesses of approximately one-quarter of the wavelength corresponding to the target resonant frequency of the device. A BAW resonator that is disposed on an acoustic mirror often is referred to as a solidly mounted resonator (SMR).
BAW resonators and the electronic circuitry that is used to sense or drive the BAW resonators typically are formed as separate components that are interconnected by an interconnection substrate, such as a printed circuit board. In one proposed approach, however, a thin film piezoelectric resonator and electronic circuitry are integrated laterally across the surface of the substrate. In general, any proposal for integrating such disparate components should give due consideration to the isolation (e.g., thermal isolation and contaminant isolation) of these components from incompatible processes. The proposal for laterally integrating the thin film piezoelectric resonator and electronic circuitry, however, does not describe how the processes that are used to fabricate the BAW resonator are isolated from the processes that are used to fabricate the electronic circuitry. Lateral integration may also require a larger die size which may result in increased device cost.